Biology 101 Module 11

1. 111-1
Chapter 11
DNA Biology
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2. 11.1 DNA AND RNA
STRUCTURE
AND FUNCTION
 In this section, the following objectives will be covered:
 Describe the structure of the DNA molecule.
 List and explain the steps in the replication of DNA.
 Compare and contrast the structure of RNA with DNA.
 List the three major types of RNA and describe their functions.

3. Controversy over whether DNA or protein was the genetic message
Experiment using viruses showed only DNA directed the formation of new viruses
It took years for investigators to conclude Mendel’s factors (genes) were
on chromosomes.
Mendel knew nothing about DNA.

4. 11-4
Alfred Hershey and Martha
Chase determined that DNA is
the genetic material.
Their experiment involved a virus
that infects bacteria, such as E.
coli.
They wanted to know which part of
the virus entered the bacterium
•Capsid made of protein
•DNA inside the capsid
Radioactive tracers showed that
DNA, not protein, enters the
bacterium and guides the
formation of new viruses.
Therefore, DNA must be the
genetic material.

6. STRUCTU
RE OF
DNA
• Race to determine the
structure
• Chargaff’s rules
• Knew DNA contains four types
of nucleotides
• Examined DNA from many
species
• The amount of A, T, G, and C
in DNA varies from species
to species.
• In each species, the amount
of A = T and the amount of G
= C.
• All nucleotides contain
phosphate, a 5-carbon sugar,
and a nitrogen-containing
base.

8. 11-8
 Rosalind Franklin was studying
the structure of DNA.
 Her data showed DNA to be a
helix with some portions
repeating over and over.

9. 11-9
 1951—James Watson and
Francis Crick set out to bring
together all the data on DNA
and build a model
 The model suggested how
replication works.
 Their model holds true today
with few changes.
 Won the Nobel Prize

10. DNA
STRUCTU
RE
• DNA structure is a double
helix, like a twisted ladder
• Deoxyribose sugar and
phosphate molecules are
bonded, forming the sides,
with the bases making up the
rungs of the ladder.
• Complementary base pairing of
A&T and G&C
• Hydrogen bonding between the
bases holds the halves of the
helix together.

11. 11-11

12. Process of copying DNA before cell division
Two strands separate
•Each strand serves as a template for a new strand
Semiconservative—each new DNA molecule is
made of one parent strand and one new strand
Replication requires
•Unwinding—helicase
•Complementary base pairing
•Joining—DNA polymerase and DNA ligase
New DNA molecule exactly identical to
original molecule

13. Parent strand unwinds and separates by
actions of helicase
New strands form through
complementary base pairing by actions of
DNA polymerase.
DNA ligase seals any breaks in the sugar-
phosphate backbone.
New DNA molecule will be half old and
half new
New DNA molecule will be exactly
identical to original molecule

14. 11-14

15. DNA
REPLICAT
ION IN
EUKARYO
TES
In eukaryotes, DNA replication
begins at numerous origins of
replication.
• Forms “replication bubbles”
• Bubbles spread in both directions
until they meet.

17. RNA
STRUCTU
RE AND
FUNCTIO
N
• Ribonucleic acid (RNA)
• Contains sugar ribose
• Uses uracil, not thymine
• Uses A, C, and G like DNA
• Single-stranded
• Three major types
• Messenger RNA (mRNA)
• Transfer RNA (tRNA)
• Ribosomal RNA (rRNA)

19. 11-19
S I MILARITIES O F D NA AND RNA
Both are composed of nucleotides.
Both are nucleic acids.
D I FFERENCES BETWEEN D NA AND RNA
Both have four different types of bases.
Both have a sugar-phosphate backbone.
DNA RNA
Found in nucleus Found in nucleus and
cytoplasm
Genetic material Helper to DNA
Sugar is deoxyribose. Sugar is ribose.
Bases are A,T,C,G. Bases are A,U,C,G.
Double-stranded Single-stranded
DNA is transcribed (to give a
variety of RNA molecules).
mRNA is translated
(to make proteins).

20. THREE
TYPES
OF RNA
• Messenger RNA (mRNA)
• Produced in the nucleus from DNA
template
• Carries genetic message to ribosomes
• Transfer RNA (tRNA)
• Produced in the nucleus from DNA
template
• Transfers amino acids to ribosomes
• Each type carries only one type of
amino acid
• Ribosomal RNA (rRNA)
• Produced in the nucleolus of the
nucleus from DNA template
• Joins with proteins to form ribosomes
• Ribosomes may be free or in
polyribosomes (clusters) or attached to
ER

21. 11.2 GENE
EXPRESSION
 In this section, the following objectives will be covered:
 Describe the processes of transcription and translation.
 Summarize the steps involved in gene expression and how it
uses the genetic code.

22. 11-22
• First to suggest a link
between genes and
proteins
Early 1900s, Sir
Archibald Garrod
suggests a
relationship between
inheritance and
metabolic diseases
• Information flows from
DNA to RNA to protein
DNA provides a
blueprint to
synthesize proteins.

23. 11-23
Transcription
•DNA serves as template to make mRNA
Translation
•mRNA directs sequence of amino acids in a
protein
•rRNA and tRNA assist

24. 11-24
 DNA: sequence of bases
is genetic information.
 Transcription: genetic
information is passed
from DNA to mRNA.
 Translation: amino acids
in a polypeptide are
sequenced as specified by
the template DNA strand.

25. THE
GENETIC
CODE
• Translates from nucleic acids
to amino acids
• Triplet—3 nucleotide sequence
in DNA
• Codon—3 nucleotide sequence
in mRNA
• A codon encodes a single amino
acid.
• Start and stop codons

26. 11-26
Second base U Second base C Second base A Second base G
First base U UUU phenylalanine (Phe) UCU serine (Ser) UAU tyrosine (Tyr) UGU cysteine (Cys) Third base U
First base U UUC phenylalanine (Phe) UCC serine (Ser) UAC tyrosine (Tyr) UGC cysteine (Cys) Third base C
First base U UUA leucine (Leu) UCA serine (Ser) UAA stop UGA stop Third base A
First base U UUG leucine (Leu) UCG serine (Ser) UAG stop UGG tryptophan (Trp) Third base G
First base C CUU leucine (Leu) CCU proline (Pro) CAU histidine (His) CGU arginine (Arg) Third base U
First base C CUC leucine (Leu) CCC proline (Pro) CAC histidine (His) CGC arginine (Arg) Third base C
First base C CUA leucine (Leu) CCA proline (Pro) CAA glutamine (Gln) CGA arginine (Arg) Third base A
First base C CUG leucine (Leu) CCG proline (Pro) CAG glutamine (Gln) CGG arginine (Arg) Third base G
First base A AUU isoleucine (Ile) ACU threonine (Thr) AAU asparagine (Asn) AGU serine (Ser) Third base U
First base A AUC isoleucine (Ile) ACC threonine (Thr) AAC asparagine (Asn) AGC serine (Ser) Third base C
First base A AUA isoleucine (Ile) ACA threonine (Thr) AAA lysine (Lys) AGA arginine (Arg) Third base A
First base A AUG methionine (Met) (start) ACG threonine (Thr) AAG lysine (Lys) AGG arginine (Arg) Third base G
First base G GUU valine (Val) GCU alanine (Ala) GAU aspartic acid (Asp) GGU glycine (Gly) Third base U
First base G GUC valine (Val) GCC alanine (Ala) GAC aspartic acid (Asp) GGC glycine (Gly) Third base C
First base G GUA valine (Val) GCA alanine (Ala) GAA glutamic acid (Glu) GGA glycine (Gly) Third base A
First base G GUG valine (Val) GCG alanine (Ala) GAG glutamic acid (Glu) GGG glycine (Gly) Third base G

27. • During transcription,
complementary RNA is made from
a DNA template.
• Portion of DNA unwinds and unzips
at the point of attachment of RNA
polymerase
• Bases join in the order dictated by
the sequence of bases in the
template DNA strand.
TRANSCRI
PTION

28. 11-28
 Transcription is taking
place- the nucleotides of
mRNA are joined by the
enzyme RNA polymerase in
an order complementary to
a strand of DNA.
 This mRNA transcript is
ready to be processed.

29. Newly made pre-mRNA must be processed.
• Capping and addition of poly-A tail provides stability
• Introns (non-coding) removed
• Leaves only exons (coding)
• Alternative splicing can produce different versions of mRNA
leading to different proteins.
• Now mature mRNA leaves nucleus and associates with ribosome
on cytoplasm.

30. e = exons
i = introns

31. 11-31
 Ribosomes are composed of protein and rRNA.
 Site of translation—protein synthesis
 Binds mRNA and two tRNA molecules
 P site for a tRNA attached to a peptide
 A site for newly arrived tRNA with an amino acid

32. TRANSLA
TION
OVERVIE
W
tRNA brings amino acids to
the ribosome to join with
mRNA codon
Anticodon—group of three
bases complementary to a
specific codon of mRNA
After translation is complete,
a protein contains the
sequence of amino acids
originally specified in the
DNA.

34. TRANSL
ATION
Three stages of translation in detail
• Initiation
• mRNA binds to small subunit of
ribosome
• Large subunit then joins
• Elongation
• Peptide lengthens one amino acid at a
time
• Termination
• 1 of 3 stop codons reached
• Release factor causes ribosomal
subunits and mRNA to dissociate
• Complete polypeptide released

35. 11-35
A small ribosomal subunit
binds to mRNA; an initiator
tRNA pairs with the mRNA
start codon AUG. The large ribosomal subunit
completes the ribosome.
Initiator tRNA occupies the
P site. The A site is ready
for the next tRNA.

36. 11-36
1. A tRNA-amino acid
approaches the ribosome
and binds at the A site.
2. Two tRNAs can be at a
ribosome at one time;
the anticodons are
paired to the codons.
3. Peptide bond formation
attaches the peptide
chain to the newly
arrived amino acid.
4. The ribosome moves forward; the
“empty” tRNA exits from the E
site; the next amino acid-tRNA
complex is approaching the
ribosome.

37. 11-37
The release factor hydrolyzes the bond
between the last tRNA at the P site and
the polypeptide, releasing them. The
ribosomal subunits dissociate.
The ribosome comes to a stop
codon on the mRNA. A release
factor binds to the site.

39. 11.3 GENE
REGULATION
 In this section, the following objectives will be covered:
 Explain the operation of the lac operon in prokayotes and how it
controls gene expression.
 Describe the levels of control of gene expression in eukaryotes.

40. 11-40
GENE REGULATION
There are levels of gene
expression control:
• Body contains many cells that
differ in structure and
function
• Only certain genes are active
in cells that perform
specialized functions
• Housekeeping genes govern
functions common to all cells
• Activity of selected genes
accounts for specialization
Gene expression in
specialized cells

41. •E.coli does not normally transcribe the genes of the lac operon.
•When lactose is not present, repressor binds to the operator and RNA polymerase
cannot attach to the promoter and inhibits transcription
Operon—cluster of bacterial genes along with DNA control sequence
François Jacob and Jacques Monod—Nobel Prize 1961 for lac operon
If we drink milk, E. coli immediately begins to make three enzymes
needed to metabolize lactose.
Escherichia coli lives in our intestine and can quickly adjust its
enzymes according to what we eat.

42. When lactose is present, it binds to the repressor.
• Repressor is inactivated and cannot attach to operator
• RNA polymerase can bind and transcription occurs.
• System can also work for genes normally turned on
• Binding of tryptophan (gene for synthesis normally on) causes
operator to be turned off

43. a.Lactose is absent-operon is
turned off.
Enzymes needed to
metabolize lactose are not
produced.
a.Lactose is present-operon is
turned on.
Enzymes needed to
metabolize lactose are
produced.

44. Each gene has its own promoter.
Employ a variety of mechanisms
•Affect whether gene is expressed, speed
of expression, and length of expression
Some mechanisms occur in
nucleus and others in cytoplasm
•Nucleus—chromatin condensation,
mRNA transcription, and mRNA
processing
•Cytoplasm—delay of transcription,
duration of mRNA or protein

46. CHROMAT
IN
CONDENS
ATION
• Way to keep genes turned off
• More tightly compacted = less
gene expression
• Heterochromatin—dark
staining regions of tightly
compacted, inactive chromatin
• Barr body—second X
chromosome in mammalian
females
• Which X is inactivated? —
female tortoiseshell cat

47. 11-47
© Photodisc/Getty RF
Females have two X chromosomes.
One X chromosome is inactivated in
each cell. Which one is by chance.
Coats of calico cats
have patches of orange
and black.

48. EUCHRO
MATIN
• Unpacked heterochromatin
• Contains active genes
• Nucleosome—portion of DNA
wrapped around histones
• Transcription activator pushes
aside histones so that
transcription can begin.

50. Same principles as prokaryotic transcription
but with more regulatory proteins per gene
Allows for greater control but also a greater
chance for malfunction
Transcription factors—DNA-binding proteins
that help RNA polymerase bind to a
promoter
• Several needed in each case, need all of
them
• Form complex that helps pull apart helix
and helps position RNA polymerase
• Same ones used in different combinations
• If one is defective, it can have serious
effect—Huntington disease
• Speed up transcription
• Bind to enhancer region of DNA
DNA
TRANSCRI
PTION IN
EUKARYO
TES

52. 11-52
 Possible for a single
transcription factor to
have dramatic effect on
gene expression
 MyoD alone can
activate the genes
necessary for
fibroblasts to become
muscle cells.
 Ey can bring about
the formation of a
complete eye in flies.

53. • After transcription, introns must
be removed and exons spliced
together.
• Alternative mRNA processing
allows cells to produce multiple
proteins from the same gene by
changing the way exons are joined.
• Fruit fly DScam gene can produce
over 38,000 different combinations
MRNA
PROCESSI
NG

55. MRNA
TRANSLA
TION
• Cytoplasm contains proteins
that determine whether
translation takes place.
• Environmental conditions can
delay translation.
• Red blood cells do not produce
hemoglobin unless heme is
available.
• The longer mRNA remains in
the cytoplasm before it is
broken down, the more gene
product is produced.
• It can be affected by length of
poly A tail or presence of
hormones.

56. • Some proteins are not active
immediately after synthesis.
• Insulin must be processed
before it is an active form.
• Allows protein’s activity to be
delayed until needed

57. In multicellular organisms, cells
are constantly sending out
chemical signals that influence the
behavior of other cells.
• During development, signals determine
what a cell becomes.
• Later, they help coordinate growth and
daily functions.
Cell-signaling pathway
• Begins when chemical signal binds to
receptor on target cell plasma membrane
• Initiates signal transduction pathway
• End product affects cell (not original signal
itself)

58. CELL-SIGNALING

59. CHAPTER 11 OBJECTIVE
SUMMARY
 You should now be able to:
 1. Describe the structure of the DNA molecule.
 2. List and explain the steps in the replication of DNA.
 3. Compare and contrast the structure of RNA with DNA.
 4. List the three major types of RNA and describe their
functions.
 5. Describe the processes of transcription and translation.
 6. Summarize the steps involved in gene expression and
how it uses the genetic code.
 7. Explain the operation of the lac operon in prokayotes
and how it controls gene expression.
 8. Describe the levels of control of gene expression in
eukaryotes.